The NHL’s black-and-white delay-of-game rule found a gray area late in regulation, then tipped the balance of the game twice in overtime. The Washington Capitals held firm when they were a man down, then won it on Mike Green’s latest extra-time winner, topping the Rangers 1-0 Saturday to take a 2-0 series lead in the Eastern Conference playoffs.

It’s the eighth career overtime goal — and first in the postseason — for the defenseman whose more well-known nickname is “Game Over Green.”

“When it gets to overtime and guys start to get the shakes a little bit, he’s still calm Mike Green,” teammate Karl Alzner said. “So he’s able to find those goals. We call him ‘Casual Mike’ every now and then.”

Braden Holtby made 24 saves for his first career playoff shutout for the Capitals and has stopped 59 of 60 shots in the series.

Game 3 is Monday in New York.

Green got his chance because the Capitals’ power play — the best in the NHL during the regular season — finally returned to the ice thanks to the rule that sends a player to the box when he “shoots or bats” the puck “directly” over the glass while in his defensive zone.

The Rangers had done a better job staying out of the box after taking too many minors in Game 1, but the officials had no choice when defenseman Ryan McDonagh clearly committed the error 7:09 into overtime.

“Just got a little too under it,” McDonagh said.

On only their second man-advantage of the game — and first since the first period — Green nailed a one-timer from high in the slot on a feed from Mike Ribeiro precisely at the eight-minute mark of the extra period.

Contrast that with the New York power play that started 1:51 into overtime, after Steve Oleksy was whistled for the over-the-glass miscue. The Rangers failed to get a shot on goal during their two minutes of 5-on-4 — or at any point in the extra period.

“It comes down to: They score on their power play and we don’t,” Rangers captain Ryan Callahan said.

New York also had a power play late in regulation after Troy Brouwer slashed Rick Nash. The Rangers went 0 for 3 on the power play for the game and are 0 for 7 for the series.

“We’re just too stagnant,” New York coach John Tortorella said. “We’re almost paralyzed.”

The Rangers nearly had another power-play chance in the final minute of regulation, when Alzner swiped at the puck and put it over the glass. Holtby thought for sure that his teammate was headed to the box, but the officials conferred and decided not to make the delay call. Alzner said it was because they decided he had tipped the puck.

“I was thinking about that last night,” Alzner said. “I was thinking if that play ever happened, what would the call be? And I guess it’s discretionary, whatever. … It’s kind of a weird coincidence.”

The Rangers bit their tongue about it after the game.

“There’s no use talking about it now,” Callahan said. “I mean, it doesn’t matter. Just move on.”

Pucks-over-glass debates aside, the game consisted mostly of Henrik Lundqvist and Holtby kicking, swiping, catching and otherwise getting in the way of the puck. Lundqvist finished with 37 saves.

“He was big for us again,” Rangers defenseman Dan Girardi said. “And it would have been nice to get the victory for him.”

A razor-thin margin in the playoffs between these teams is hardly surprising. Six of their seven games in last year’s postseason were decided by one goal, including a Rangers win that went to three overtimes. This is the third Rangers-Capitals series in three years, and five of those 14 games have required extra time to decide a winner.

The Capitals are more offensively minded this year under first-time coach Adam Oates, but the Rangers were able to mostly corral regular season goal-scoring leader Alex Ovechkin and the rest of Washington’s high-powered attack.

Lundqvist had to work harder than Holtby, but both were in top form — and caught a few breaks as well. New York’s Anton Stralman hit the crossbar about four minutes into the game. Lundqvist reacted quickly to make a kick save on Mathieu Perreault. On and on it went.

But Lundqvist couldn’t stop the game’s final shot from Green, whose 12 regular season goals led all NHL defensemen.

“I just happened to be open,” Green said. “And my goal was just to get it by that first guy and try to hit the net.”

Notes: F Derek Dorsett made his Rangers debut. He broke his collarbone March 7 while playing for the Columbus Blue Jackets and was thought to be done for the season. He was sent to New York last month at the trade deadline. F Brian Boyle returned after being sidelined since April 16 with a right leg injury. The Rangers remained without D Marc Staal (eye) and F Ryane Clowe (undisclosed). … Cs Chris Kreider and Kris Newbury were scratched to make room for Dorsett and Boyle.